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Computer Graphics and Applications, 2004. PG 2004. Proceedings. 12th Pacific Conference on

Date 6-8 Oct. 2004

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Displaying Results 1 - 25 of 52
  • Accelerated geometric queries and physical simulation using graphics processors

    Page(s): 37 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (241 KB) |  | HTML iconHTML  

    Given the increasing power and usage of commodity graphics processor units (GPUs), promising potential exists for exploiting the fast growing computational power on GPUs for general-purpose computing. We present some of our recent research on fast geometric queries and interactive physical simulation using GPUs. View full abstract»

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  • CSG tree rendering for point-sampled objects

    Page(s): 160 - 168
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (582 KB) |  | HTML iconHTML  

    This paper presents an algorithm for rendering of point-sampled CSG models. The approach works with arbitrary CSG trees of surfel models with arbitrary sampling densities. Edges and corners are rendered by reconstructing the involved surfaces separately. The reconstructed surfaces are clipped at intersections. This way, blurring at any magnification is avoided. As opposed to existing methods, which resample surfaces close to object intersections, the proposed approach preserves the original object representation. Since no resampling is needed, dynamic scenes can be handled very flexible. Complex intersections involving any number of objects can be rendered. View full abstract»

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  • GPU-based tolerance volumes for mesh processing

    Page(s): 237 - 243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (573 KB) |  | HTML iconHTML  

    In an increasing number of applications triangle meshes represent a flexible and efficient alternative to traditional NURBS-based surface representations. Especially in engineering applications it is crucial to guarantee that a prescribed approximation tolerance to a given reference geometry is respected for any combination of geometric algorithms that are applied when processing a triangle mesh. We propose a simple and generic method for computing the distance of a given polygonal mesh to the reference surface, based on a linear approximation of its signed distance field. Exploiting the hardware acceleration of modern GPUs allows us to perform up to 3M triangle checks per second, enabling real-time distance evaluations even for complex geometries. An additional feature of our approach is the accurate high-quality distance visualization of dynamically changing meshes at a rate of 15M triangles per second. Due to its generality, the presented approach can be used to enhance any mesh processing method by global error control, guaranteeing the resulting mesh to stay within a prescribed error tolerance. The application examples that we present include mesh decimation, mesh smoothing and freeform mesh deformation. View full abstract»

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  • Real-time voxelization for complex polygonal models

    Page(s): 43 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (878 KB) |  | HTML iconHTML  

    In this paper, we present an efficient voxelization algorithm for complex polygonal models by exploiting newest programmable graphics hardware. We first convert the model into three discrete voxel spaces according to its surface orientation. The resultant voxels are encoded as 2D textures and stored in three intermediate sheet buffers called directional sheet buffers. These buffers are finally synthesized into one worksheet, which records the volumetric representation of the target. The whole algorithm traverses the geometric model only once and is accomplished entirely in GPU (graphics processing unit), achieving real-time frame rate for models with up to 2 million triangles. View full abstract»

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  • Direct anisotropic quad-dominant remeshing

    Page(s): 207 - 216
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1887 KB) |  | HTML iconHTML  

    We present an extension of the anisotropic polygonal remeshing technique developed by Alliez et al. (2003). Our algorithm does not rely on a global parameterization of the mesh and therefore is applicable to arbitrary genus surfaces. We show how to exploit the structure of the original mesh in order to perform efficiently the proximity queries required in the line integration phase, thus improving dramatically the scalability and the performance of the original algorithm. Finally, we propose a technique for producing conforming quad-dominant meshes in isotropic regions as well by propagating directional information from the anisotropic regions. View full abstract»

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  • Snaking across 3D meshes

    Page(s): 87 - 93
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1339 KB) |  | HTML iconHTML  

    We present a method of moving snake curves over 3D meshes. Our snake is made from the vertices of a triangular mesh, so it never leaves the 3D surface, eliminating any need for mapping on to ID and subsequent remapping on to the 3D mesh. Our snake finds features related to Gaussian curvature, or ridges and valleys. We move each vertex of the snake to one of its neighbor vertices on the mesh, while reducing the energy of the snake, which expresses distance from a feature, by means of a greedy optimization. This is fast enough to support real-time interaction. We handle changes of snake topology using 3D versions of methods originally developed for images. These can handle collisions within the snake, and hence split the snake and find multiple features. We demonstrate the performance of our algorithm on several example meshes, including human faces. View full abstract»

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  • Personalised real-time idle motion synthesis

    Page(s): 121 - 130
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (677 KB) |  | HTML iconHTML  

    In this paper, we propose an animation approach based on principal component analysis that allows generating two layers of subtle motions: small posture variations and personalised change of balance. Such a motion generator is needed in many cases when one attempts to create an animation sequence out of a set of existing clips. In nature there exists no motionless character, while in computer animation we often encounter cases where no planned actions, such as waiting for another actor finishing his/her part, is implemented as a stop/frozen animation. We identify many situations where a flexible idle motion generator can help: from synchronisation of speech/body animation duration, to dynamic creation of stand still variations in between two active plays. Our approach overcomes the limitations of using a small set of existing clips as a basis for synthesizing idle motions, such as unnatural repetition of movements and difficulties to insert idle motions into an animation without breaking its continuity. A realistic animation is obtained by blending small posture variations with personalised balance shifting animations. View full abstract»

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  • NeuroEnveloping: a transferable character skin deformation technique

    Page(s): 77 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (534 KB) |  | HTML iconHTML  

    We proposed a character skin deformation method, namely neuroEnveloping. The main idea relies on employing artificial neural networks to learn how to synthesize deformable skin from example shapes paired with skeleton postures of a character. Furthermore, having encoded the deformation information in the neural networks, the skinning model can be applied for the deformation of other similar characters. The character skin is decomposed into patches according to a base control mesh which is introduced as a common platform in the proposed framework. The deformation of each patch of the character is controlled by a trained neural network. We devised an effective stitching operator to eliminate discontinuities between neighboring patches. The experimental results show that the proposed approach can generate aesthetically pleasing results at interactive speed. View full abstract»

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  • Hardware-accelerated reconstruction of polygonal isosurface representations on unstructured grids

    Page(s): 186 - 195
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    Volume visualization using isosurface extraction is a well-researched topic. Research demonstrated that even for unstructured grids peak performances of millions of tetrahedra per second can be achieved by exploiting the parallel processing capabilities of modern GPUs. In this paper we present a hardware-accelerated solution that further improves the extraction performance. In contrary to existing approaches, our technique explicitly extracts the isosurface geometry in a fragment program by rendering only a single screen-sized quadrilateral. The extracted geometry is directly written to an on-board graphics memory object allowing for direct rendering without further bus transfers. Additionally, the geometry can be manipulated by shader programs or read back to the application for further processing. Examples and application scenarios are given that can benefit from our approach. View full abstract»

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  • A data-driven approach for real-time clothes simulation

    Page(s): 257 - 266
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (799 KB) |  | HTML iconHTML  

    A data-driven approach for real-time processing of clothes, particularly suitable for simulating dresses worn by virtual characters, is proposed. It starts, prior to realtime simulation, by analyzing cloth behavior in relation to the underlying skeleton movement from a pre-simulated sequence of the cloth obtained using any high quality offline simulators. The idea is to use this analysis to find an optimal combination of physics-based simulation and geometric approximation of the simulator; potentially colliding regions are defined on the cloth such that they will hold true for the skeleton movement that closely matches that of pre-simulated sequence. At runtime, using these analyses, our simulation process provides both visually pleasing results and performance, as long as the motion of the character remains sufficiently close to the original sequence used for the pre-computation. The key contributions of this paper are (1) efficient collision handling that prunes out potentially colliding objects by using the off-line simulation sequence as examples; (2) data-driven fix-up process for the coarse mesh simulation that deduces the gross behavior of the cloth; and (3) geometric approximation of the fine mesh deformation, responsible for details in the shape of the cloth such as wrinkles. View full abstract»

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  • Perceptually based approach for planar shape morphing

    Page(s): 111 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (594 KB) |  | HTML iconHTML  

    This paper presents an approach for establishing vertex correspondences between two planar shapes. Correspondences are established between the perceptual feature points extracted from both source and target shapes. A similarity metric between two feature points is defined using the intrinsic properties of their local neighborhoods. The optimal correspondence is found by an efficient dynamic programming technique. Our approach treats shape noise by allowing discarding small feature points, which introduces skips in the traversal of the dynamic programming graph. Our method is fast, feature preserving, and invariant to geometric transformations. We demonstrate the superiority of our approach over other approaches by experimental results. View full abstract»

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  • Pattern oriented remeshing for Celtic decoration

    Page(s): 199 - 206
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3067 KB) |  | HTML iconHTML  

    Decorating arbitrary meshes with Celtic knots requires polygonal meshes with regular connectivity and close to regular face geometry. Because these properties are often irregular, especially in scanned or reconstructed models, the Celtic knots produced may be erratic and undesirable. In this paper we remesh models based on planar tilings defined by the user. Such pattern-oriented surfaces allow us to decorate models with attractive Celtic knots in a consistent fashion and may be applicable to a large number of algorithms that are sensitive to mesh structure. View full abstract»

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  • Segmentation of 3D meshes through spectral clustering

    Page(s): 298 - 305
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (698 KB) |  | HTML iconHTML  

    We formulate and apply spectral clustering to 3D mesh segmentation for the first time and report our preliminary findings. Given a set of mesh faces, an affinity matrix which encodes the likelihood of each pair of faces belonging to the same group is first constructed. Spectral methods then use selected eigenvectors of the affinity matrix or its closely related graph Laplacian to obtain data representations that can be more easily clustered. We develop an algorithm that favors segmentation along concave regions, which is inspired by human perception. Our algorithm is theoretically sound, efficient, simple to implement, andean achieve high-quality segmentation results on 3D meshes. View full abstract»

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  • Mesh modelling with curve analogies

    Page(s): 94 - 98
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (446 KB) |  | HTML iconHTML  

    Modelling by analogy has become a powerful paradigm for editing images. Using a pair of before- and after-example images of a transformation, a system that models by analogy produces analogous transformations on arbitrary new images. This paper brings the expressive power of modelling by analogy to meshes. To avoid the difficulty of specifying fully 3D example meshes, we use curve analogies to produce changes in meshes. We apply analogies to families of curves on an object's surface, and use the filtered curves to drive a transformation of the object. We demonstrate a range of filters, from simple local feature elimination/addition, to more general frequency enhancement filters. View full abstract»

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  • Real-time 3D fluid simulation on GPU with complex obstacles

    Page(s): 247 - 256
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    In this paper, we solve the 3D fluid dynamics problem in a complex environment by taking advantage of the parallelism and programmability of GPU. In difference from other methods, innovation is made in two aspects. Firstly, more general boundary conditions could be processed on GPU in our method. By the method, we generate the boundary from a 3D scene with solid clipping, making the computation run on GPU despite of the complexity of the whole geometry scene. Then by grouping the voxels into different types according to their positions relative to the obstacles and locating the voxel that determines the value of the current voxel, we modify the values on the boundaries according to the boundary conditions. Secondly, more compact structure in data packing with flat 3D textures is designed at the fragment processing level to enhance parallelism and reduce execution passes. The scalar variables including density and temperature are packed into four channels of texels to accelerate the computation of 3D Navier-Stokes equations (NSEs). The test results prove the efficiency of our method, and as a result, it is feasible to run middle-scale problems of 3D fluid dynamics in an interactive speed for more general environment with complex geometry on PC platform. View full abstract»

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  • Intelligent mesh scissoring using 3D snakes

    Page(s): 279 - 287
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1345 KB) |  | HTML iconHTML  

    Mesh partitioning and parts extraction have become key ingredients for many mesh manipulation applications both manual and automatic. In this paper, we present an intelligent scissoring operator for meshes which supports both automatic segmentation and manual cutting. Instead of segmenting the mesh by clustering, our approach concentrates on finding and defining the contours for cutting. This approach is based on the minima rule, which states that human perception usually divides a surface into parts along the contours of concave discontinuity of the tangent plane. The technique uses feature extraction to find such candidate feature contours. Subsequently, such a contour can be selected either automatically or manually, or the user may draw a 2D line to start the scissoring process. The given open contour is completed to form a loop around a specific part of the mesh, and this loop is used as the initial position of a 3D geometric snake. The snake moves by relaxation until it settles to define the final scissoring position. This process uses several fundamental geometric mesh attributes, such as curvature and centricity, and enables both automatic segmentation and an easy-to-use intelligent-scissoring operator. View full abstract»

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  • Frequency-based environment matting

    Page(s): 402 - 410
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB) |  | HTML iconHTML  

    Environment matting is a technique to extract the environment matte which is used to describe how an object reflects and refracts the environment light. In this paper, we propose a novel environment matting method to obtain the environment matte of a real scene. Previous methods use different backdrops as the calibration patterns and search for the environment matte in the spatial domain. In our method, however, a series of background images displayed on a screen sequentially in time are interpreted as signals. The frequency similarity of these signals is used as the searching criterion. The frequencies of these signals are not changed when they interact with the foreground objects and thus can be used to extract the environment matte. While using correspondence in the spatial domain in existing approaches is prone to error, using frequency correspondence is not. Thus, our approach is robust to noise and can easily deal with some of the complex light transport phenomena which cannot be easily handled using current methods. The experimental results are very encouraging. View full abstract»

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  • Fitting subdivision surfaces to unorganized point data using SDM

    Page(s): 16 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1560 KB) |  | HTML iconHTML  

    We study the reconstruction of smooth surfaces from point clouds. We use a new squared distance error term in optimization to fit a subdivision surface to a set of unorganized points, which defines a closed target surface of arbitrary topology. The resulting method is based on the framework of squared distance minimization (SDM) proposed by Pottmann et al. Specifically, with an initial subdivision surface having a coarse control mesh as input, we adjust the control points by optimizing an objective function through iterative minimization of a quadratic approximant of the squared distance function of the target shape. Our experiments show that the new method (SDM) converges much faster than the commonly used optimization method using the point distance error function, which is known to have only linear convergence. This observation is further supported by our recent result that SDM can be derived from the Newton method with necessary modifications to make the Hessian positive definite and the fact that the Newton method has quadratic convergence. View full abstract»

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  • Interactive caustics using local precomputed irradiance

    Page(s): 143 - 151
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (986 KB) |  | HTML iconHTML  

    Bright patterns of light focused via reflective or refractive objects onto matte surfaces are called "caustics". We present a method for rendering dynamic scenes with moving caustics at interactive rates. This technique requires some simplifying assumptions about caustic behavior allowing us to consider it a local spatial property which we sample in a preprocessing stage. Storing the caustic locally limits caustic rendering to a simple lookup. We examine a number of ways to represent this data, allowing us to trade between accuracy, storage, run time, and precomputation time. View full abstract»

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  • Modeling hairy plants

    Page(s): 217 - 226
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2033 KB) |  | HTML iconHTML  

    The appearance of computer generated plants has improved significantly due to advances in both modeling and rendering. In this paper we describe a system that further improves the appearance of CG plants by including the tiny hairs that cover many plant organs. A plant skeleton is generated using an L-system and graphically interpreted using generalized cylinders. The individual hairs are then mapped onto the surfaces and boundary edges of the mesh. Hair properties are specified and adjusted according to positional information. Sample images included in the paper illustrate the impact of hairs on the appearance of rendered plants. View full abstract»

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  • Colored pencil filter with custom colors

    Page(s): 329 - 338
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB) |  | HTML iconHTML  

    This paper presents a new technique for automatically converting digital images into colored pencil drawings. In real colored pencil drawing, artists use different colors for different regions, and add pure colors directly onto paper to build the target color through optical blending. To support such effect, our technique extends the existing technique for reproducing color image with custom inks to automatically select the best color set for individual regions in a source image. Then layers of stroke image for each color are generated and superimposed with the Kubelka-Munk optical compositing model. We also allow users to specify regions and to customize the color set for a specified region interactively. The proposed technique can be easily extended to simulate other artistic media featured with optical color blending, such as pastel and wax crayons. View full abstract»

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  • Controllable single-strip generation for triangulated surfaces

    Page(s): 61 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1719 KB) |  | HTML iconHTML  

    In this paper, we introduce a method to represent a given triangular model using a single triangle strip. Since this problem is NP-complete, we break the limitation by splitting adjacent triangles when necessary. The common edge is split at the mid-point, and the newly formed triangles are coplanar with their parent triangles. Hence, the resulting geometry of the model is visually and topologically identical to the original triangular model. Our method can develop any edge-connected oriented 2-manifold of arbitrary topology, with or without boundary, into a single strip. Our stripification method can be controlled to start and end at triangles incident on specific vertices. Further, an acyclic set of edges of the input model can be marked as "constraint edges" and our method can generate a single strip that does not cross over these edges, but still cover the whole model. View full abstract»

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  • Non-photorealistic real-time rendering of characteristic faces

    Page(s): 339 - 347
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1958 KB) |  | HTML iconHTML  

    We propose a system for real-time sketching of human faces. On the basis of a three-dimensional description of a face model, characteristic line strokes are extracted and represented in an artistic way. In order to enrich the results with details that cannot be determined analytically from the model surface and anchor strokes are supplemented interactively and are maintained during animation. Because of the real-time ability of our rendering pipeline the system is suitable for interactive facial animation. Thus, interesting areas of application within the range of the virtual avatars are possible. View full abstract»

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  • Discontinuous free form deformations

    Page(s): 227 - 236
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1486 KB) |  | HTML iconHTML  

    Contemporary deformation tools let designers modify the geometry of deformed models. This approach can be restrictive if the designer wants to incorporate holes or gaps into a model while deforming it into a different shape. This work presents a variant of FFD that would let the designer incorporate isoparametric discontinuities into the deformation function. The input model is automatically split at these discontinuities, allowing the deformed model to reflect topological discontinuity changes. We demonstrate the deformation algorithm using two different applications. The first application wraps a moving model around obstacles in a scene, splitting and then reforming it. The second application works locally, enabling the end-user to insert arbitrarily shaped cuts into the surface of the model. View full abstract»

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  • Density measure for line-drawing simplification

    Page(s): 309 - 318
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1617 KB) |  | HTML iconHTML  

    We present an approach for clutter control in NPR line drawing where measures of view and drawing complexity drive the simplification or omission of lines. We define two types of density information: the a-priori density and the causal density, and use them to control which parts of a drawing need simplification. The a-priori density is a measure of the visual complexity of the potential drawing and is computed on the complete arrangement of lines from the view. This measure affords a systematic approach for characterizing the structure of cluttered regions in terms of geometry, scale, and directionality. The causal density measures the spatial complexity of the current state of the drawing as strokes are added, allowing for clutter control through line omission or stylization. We show how these density measures permit a variety of pictorial simplification styles where complexity is reduced either uniformly, or in a spatially-varying manner through indication. View full abstract»

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